Forming substantially rectangular articles from preforms of polyalkylene terephthalate

ABSTRACT

In forming hollow, molecularly oriented articles having substantially rectangular cross sections from thermoplastic preforms by a method which includes distending the preforms in a mold while at molecular orientation temperature, the improvement providing improved material distribution in regions furthest from the central axes of the articles (e.g. in the corner areas) when the thermoplastic is moldable polyalkylene terephthalate having an inherent viscosity of at least 0.55 which involves limiting the corner definition ratio to between about 2 to about 14 and the circular deviation ratio to no greater than about 2.4 at the cross section during distension and controlling axial and maximum radial stretch of the preforms within predetermined limits.

CROSS REFERENCE TO RELATED APPLICATION

Improvements In Forming Non-Cylindrical Articles From Preforms OfPolyalkylene Terephthalate, Purushottam D. Agrawal, U.S. Ser. No.971,398, filed Dec. 20, 1978.

BACKGROUND OF THE INVENTION

This invention relates to forming hollow, molecularly oriented articlessuch as containers of polyalkylene terephthalate such as polyethyleneterephthalate (PET), and more particularly to improvements in a preformprocess for forming articles of such material having certain non-roundcross sections wherein material distribution is improved in the vicinityof the ends of the sides.

Containers of molecularly oriented PET are known and desirable forpackaging because of superior clarity, impact strength and barrierproperties. Prior to this invention, configurations of such containershave been largely limited to circular yet it is frequently desirable foraesthetics and functional reasons such as space conservation to be ableto blow mold non-circular containers of rectangular, e.g. square, shapewith good material thickness uniformity in the peripheral direction.

Attempts in the past to form non-round configurations from commoditythermoplastics such as polyethylene and polypropylene in a processwherein prior-shaped preforms are conditioned to molecular orientationtemperature before distension in the blow mold entailed establishingspecial conditions to promote wall thickness uniformity between areasfurthest from the lengthwise axis and areas close to the axis. Asdisclosed in U.S. Pat. No. 3,950,459, such systems usually involvedestablishing temperature differences in the circumferential direction ofthe preforms such that portions to expand less were cooler and thereforewould stretch less than hotter portions which were to stretch more inthe blow mold. If such temperature difference is not well establishedexcessive thinning or even blow out at the extremities of the crosssection could be expected to occur. Needless to say, consistent accurateprovision of such a differential does not facilitate simplicity of thepreform heat treating process.

SUMMARY OF THE INVENTION

Now, however, process improvements have been developed to facilitatefabrication of non-round hollow articles of polyalkylene (e.g.polyethylene) terephthalate.

Accordingly, it is a principal object of this invention to provideimprovements in a process for forming non-round, molecularly oriented,hollow articles such as containers from polyalkylene terephthalate, e.g.PET, thermoplastic materials, which result in improved materialthickness distribution in regions furthest from the lengthwise axis ofnon-round cross sections of the article.

Another object of this invention is to recognize and use the inherentmechanical properties of PET to advantage to promote such improvedmaterial distribution.

A specific object is to recognize and define relationships betweenforming parameters and the extent to which the cross sectional shape canbe varied in blowing substantially rectangular molecularly oriented PETcontainers with good contour definition in the vicinity of the extremesof the container cross section, e.g. in the rounded corners.

Other objects of this invention will in part be obvious and will in partappear from the following description and claims.

These and other objects are provided in the method of forming amolecularly oriented hollow article having a substantially rectangularcross section from a preform of thermoplastic material, which includesdistending the preform in a mold while at molecular orientationtemperature, by providing the improvement wherein the thermoplasticmaterial is moldable polyalkylene terephthalate having an inherentviscosity of at least about 0.55 and the forming operation comprises, incombination, the steps of limiting the corner definition ratio tobetween about 2 to about 14 and the circular deviation ratio to nogreater than about 2.4 at the cross section during such distending andcontrolling such distending according to the relations: ##EQU1##wherein: A is between about 5 to about 100 and B is no greater thanabout 334.

BRIEF DESCRIPTION OF THE DRAWINGS

In describing the overall invention, reference will be made to theaccompanying drawings wherein:

FIG. 1 is a graphical representation portraying dimensional limits ofcertain rectangular containers which can be effectively formed accordingto the invention;

FIG. 2 is a graphical representation of the relationship of the level ofstretch which should be used according to the invention in formingrectangular containers having the dimensions shown on the ordinate ofFIG. 1;

FIG. 3 is a stress/strain diagram at a stated strain rate for PET at astated temperature;

FIG. 4 is a vertical elevational view of a container formable from apreform according to this invention;

FIG. 5 is a schematic sectional view along 5-5 of FIG. 4;

FIG. 6 is a schematic elevational view of a stretch-blow assemblycapable of converting the preform outlined in FIG. 4 into the containertherein shown; and

FIG. 7 is a view similar to FIG. 5 of an alternative container crosssection.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

In forming containers of polyethylene terephthalate having non-roundcross sections (such as substantially rectangular including square)either throughout most or all of the length or at least at one or morehorizontal sections along such length, by distending circular preformsat molecular orientation temperature in a blow mold, such cross sectionscan be formed with good wall thickness uniformity because of themechanical properties of the PET material without relying on acircumferential temperature gradient in the material of the preforms.

More particularly, preform 10, shown in outline in FIG. 4, is circularin cross section and is to be expanded in blow mold 40 (FIG. 6) having acavity configuration conforming in outline to that of bottle 12 (FIG. 4)having maximum rectangular cross section 14 (FIG. 5) along its lengthlying in a plane perpendicular to its longitudinal axis. During blowingat molecular orientation temperature, preform 10 will initially distendradially until its outer surface first contacts the mold cavity wall inthe vicinity of the ends of minor diameter or axis 16 (FIG. 5). Suchinitial expansion is illustrated schematically in FIG. 5 by the seriesof successively larger concentric circles shown in outline form with theinitial contact just referred to occurring at 15a, 15b. Furtherexpansion to complete formation of the rectangular shape stretches thefree sides, schematically shown at 24, 26 in FIG. 5, of the partiallyexpanded circular form which have not yet contacted the cavity surfaceoutwardly toward the extremes of major axis 18 to eventually form shortwalls 20a, 20b at the ends of such axis. This further expansion drawsplastic from the portions of the circumference of the circular shapewhich have already contacted the mold wall. The latter portions of thepreform (i.e. the regions including 15a and 15b in FIG. 5) will benecessarily cooler than free, unrestrained portions 24, 26 at the endsof the developing rectangular shape, since the mold cavity walls arecooled in conventional manner by circulation of a heat transfer mediumthrough channels in the mold just beneath the cavity surface. PETmaterial by nature exhibits significant resistance to stretch atmolecular orientation forming temperatures. Thus, as indicated in FIG.3, at a temperature of 200° F. (93° C.), and a 10% per second strainrate, a stress of 450 psi is required to achieve 200 percent stretch.For an additional 50 percent increase in stretch (from 200 to 250percent along the x axis in FIG. 3) a stress increase of 200 psi (14kg./cm.²) (along the y axis) is required. At 200 percent stretch astress of 450 psi (31.5 kg./cm.²) is needed while at 250 percent, astress of 650 psi (45.5 kg./cm.²) is needed. This indicates a sharpincrease in stress for relatively low percent stretch which has beenfound to cause a strain hardening effect at the 10 percent per secondstrain rate. Under actual container manufacturing conditions, however,strain rates on the order of 200 percent per second are more realisticin achieving economical blow molding cycle times. Compared to stressrequirements at the 10 percent per second strain rate, at a 200 percentper second strain rate it is expected that PET will exhibit an even moresevere rise in stress to achieve a relatively low percent stretch. Thisstrain hardening characteristic of PET facilitates formation of roundedcorners in rectangular sections of relatively uniform thickness in thatafter the polymer is stretched a given amount, the force required forfurther stretching substantially increases and at that point morematerial will be stretched out of areas not previously stretchedmuch--i.e. the initially relatively thick portions in the vicinity of15a and 15b in FIG. 5 which have stretched only to the ends of minoraxis 16. This self-adjusting nature of PET which is reflected in apulling of material out of regions 15a and 15b to provide material whicheventually forms walls 20a, 20b and corners 21 results in an improveddegree of wall thickness uniformity in a substantially rectangularconfiguration.

In comparison, for comparable amounts of stretch and stretch rates witha thermoplastic material having a relatively flat stress/strain curve,for example a nitrile polymer such as a 70/30 weight percentacrylonitrile/styrene material, stress buildup will not increase sharplywith strain. This means that material for walls forming sides at theends of the major axis will not be pulled out of the already shaped andpartially chilled plastic at the ends of the minor axis with the resultthat the thickness at the free expanding ends will continue to decreaseas the plastic moves towards the ends of the major axis. This can leadto fracture in the vicinity of the extremes of the major axis ifstretching is excessive or else substantial local thinning of the wallthickness versus that in the vicinity of the ends of the minor axis.

The tendency of PET to strain harden, however, imposes restrictions onthe amount of definition achievable in highly stretched areas such as inthe vicinity of and including rounded corners, 21a, 21b, 21c and 21d(FIG. 5) of a substantially rectangular cross section. In accordancewith the invention, for containers having a substantially rectangular(including square) cross section a relationship has been establishedbetween (a) corner definition ratio (b) circular deviation ratio (c)percent axial stretch and (d) percent maximum radial stretch which, whenfollowed, will provide excellent definition in highly stretched corneredareas of containers made of polyalkylene terephthalate such as PETthermoplastic materials. Such relationships are graphically depicted inFIGS. 1 and 2 and comprise limiting during stretching the cornerdefinition ratio to between about 2 to about 14 and the circulardeviation ratio to no greater than about 2.4. For purposes of thepresent invention, corner definition ratio is defined as two times themaximum distance between the lengthwise axis at the planar cross sectionof the finished rectangular configuration (or longitudinal axis 34 ofthe preform when mounted initially in the mold as at 10 in FIG. 6) andthe mold cavity surface defining a planar side of the rectangular shapedivided by the radius of the rounded corner. For the configuration ofFIG. 5, such corner definition ratio is represented by two timesdistance 22 divided by R₁. For the symmetrical substantially squarecross section of FIG. 7, such corner definition ratio is distance 24plus distance 28 divided by R₂. The circular deviation ratio is definedas two times the maximum distance between the lengthwise axis at theplanar cross section of the finished rectangular configuration (orlongitudinal axis 34 of the preform when mounted initially in the moldas at 10 in FIG. 6) and the mold cavity defining a planar side of therectangular shape divided by two times the minimum distance between thelengthwise axis at the planar cross section of the finished rectangularconfiguration (or longitudinal axis 34 of the preform when mountedinitially in the mold as at 10 in FIG. 6) and the mold cavity defining aplanar side of the rectangular shape. For the configuration of FIG. 5,such circular deviation ratio is major diameter 18 or two times distance22 divided by minor diameter 16 whereas for the square configuration ofFIG. 7 such ratio will always be one since distances 24 and 28 areequal.

With respect to blowing rectangular as compared with other crosssections such as oval, the corner definition to circular deviation ratiolimits will be wider for rectangular shapes since the expanding portionsof the preform after initial contact with the mold (i.e. the portions oneither side of regions 15a and 15b in FIG. 5) will be able to stretchmore before contacting the walls of the rectangular cross section. Forexample, with respect to FIG. 5, the plastic will be able to freelyextend through region 23 before contacting the mold surface whereas suchadditional expansion in an area equivalent to 23 could not occur if thecavity was oval as such oval cavity outline is schematically depicted byshort phantom line 25 in FIG. 5. Because of this the previouslydescribed cooling effect associated with mold wall contact will be lesspronounced with rectangular shapes thus facilitating formation ofrelatively shallow radii R₁, R₂ in FIGS. 5 and 7 in rectangularconfigurations.

Further in accordance with the invention, preform distension in the moldis controlled according to the relations: percent axial stretch (A)equals article length (30 in FIG. 4) minus preform length (11 in FIG. 4)times 100 divided by preform length minus preform neck finish length (32in FIG. 4); and percent maximum radial stretch (B) equals the maximumplanar distance (22 in FIG. 5 and 24 in FIG. 7) to the mold surfacedefining a side of the rectangular shape from the preform axis (which inFIG. 6 is 34) when mounted in the mold minus the preform outsidediameter (36 in FIG. 4) times 100 divided by the preform outsidediameter wherein: A is between about 5 to about 100 and B is no greaterthan about 334. In situations where the finish is formed on the articleduring reshaping in the article blow mold, i.e. the preform does nothave a molded finish, a length equivalent to the finish length on theformed article should be used in the foregoing equation for percentaxial stretch, or if no finish is provided, a figure should be used forthe length of plastic, if any, which is not axially stretched duringfinal forming. With respect to the amount of axial stretch of theelongated preform being reshaped, this can vary along the length. Forexample, in the illustrated embodiment plastic close to the neck finishwill stretch less than that adjacent the closed end whereas that inbetween will stretch an amount intermediate these extremes. Instead ofusing the simplified foregoing equation to determine axial stretch, theterm "average" as it applies to axial stretch can be determined byconsidering the amount of axial stretch that occurs in incrementalsections of the preform length and then calculating the arithmeticaverage of such individual stretch amounts. This is facilitated byforming spaced grid markings on the unstretched preform surface, e.g. 1inch (2.54 cms.) apart, and computing individual stretch amounts bymeasuring the distance between immediately adjacent marks after axialstretching and before blowing.

Further with respect to the axial stretch parameter of FIG. 2, for agiven amount of plastic in the preform adequate to produce a containerof predetermined weight, if the initial preform is excessively long withrespect to the lengthwise axis (30 in FIG. 4) of the container, whichmeans the preform thickness is relatively small, the strain hardeningeffect because of the reduced thickness will be pronounced and this willtend against sharp formation of the desired corner radii since excessivethinning will occur as material approaches the areas of maximum stretch.In addition, when the preforms are injection molded, since PET is shearsensitive, lengthy movement of the material along a relatively elongatednarrow injection mold cavity promotes formation of acetaldehyde which isa decomposition product which can cause taste problems when thecontainers are intended to package human-consumable substances. On theother hand, if the preform is made excessively thick to offset thedisadvantages just mentioned, different problems can be expected duringinjection molding. More specifically, if the thickness is too great eventhough sections of the thickness adjacent the outer and inner surfacesare chilled relatively quickly in the injection forming mold to belowthe crystalline freezing point of the material via chilling contact withthe cooled preform injection mold and core rod to prevent formation ofcrystals and therefore cloudiness in the material, heat retained towardthe middle of such relatively thick sections tends to cause the materialto heat back up again after ejection from the mold to promote crystalformation and the cloudiness which it is desired to avoid.

FIG. 6 shows a stretch-blow assembly 38 for converting a preform 10 intomolecularly oriented container 12 having the configuration of FIG. 4.This is accomplished by first enclosing each preform 10 while within themolecular orientation temperature range for the thermoplastic materialof which it is formed within partible sections 44, 46 of conventionalblow mold 40. Next, stretching mechanism 48 is moved over the open endof blow mold 40 and preform 10 whereupon telescopic stretch rod 50 iscaused to move to extended position by a suitable mechanism, not shown,in order to force the hemispherical end of the preform 10 against baseportion 52 of blow mold 40 thereby axially stretching the body portionof the preform (13 in FIG. 4) in the manner illustrated in phantom at 54in FIG. 6. Simultaneously therewith or preferably immediatelythereafter, a blowing medium such as compressed air is admitted to theinterior of the preform through openings 56, 58 in rod 50 to stretch itradially outwardly against the mold cavity walls in the mannerpreviously described into the shape of bottle 12. Under certaincircumstances, for example those contemplating non-pressure applicationsfor the finished container, it may not be necessary to provide aseparate stretch rod in that the pressure of the blowing medium and thereduced length of the preform versus the container length may beadequate to provide the axial stretch desired.

The nature of the surface of the mold cavity against which thethermoplastic is forced into shaping engagement can have an effect onthe limits of formation along the major axis of the non-round containerbeing formed. In this respect, coating such surface with a heatinsulative material such as Teflon® in the area forming the panels ofthe container between its rounded corners can improve the ability toblow out into the short sides and into corners having relatively shallowradii--R₁ and R₂ in FIGS. 5 and 7. Such Teflon® coating apparentlyimproves slippage of the material on the coated surface and retardsexcessive heat transfer from the plastic thereby preventing prematuresetting of the material. On the other hand, if cycle time is not ofmajor concern the same effect can most likely be achieved by operatingthe molds at elevated temperature through use of a heat transfer mediumcirculating through channels in the mold providing a cavity surfacetemperature on the order of about 100° F. to 180° F. (38° to 82° C.).

Hollow articles such as containers formable according to the inventionfrom preforms 10 may vary widely in size and are preferablycharacterized in terms of weight and volume as ranging from betweenabout 0.03 to about 0.13 gms/cc of internal volume. The invention isapplicable to non-round, substantially rectangular cross sectionalconfigurations in container form wherein the latter have a volume ofbetween about 170 to 3780 cc. and preferably between about 470 to 1890cc. Though single layer articles are preferred, composite containershaving plural layers of thermoplastic material in face-adhering contactare likewise within the scope of those formable according to thisinvention as long as at least one layer comprises a major proportion(e.g. at least about 50 weight percent) of a polyalkylene terephthalate.

The invention is applicable to the shaping of moldable polyalkyleneterephthalates such as polyethylene and polybutylene terephthalate.

Polyethylene terephthalate useful in preparing the thermoplasticarticles of this invention includes polymers wherein a major proportionsuch as about 50 and preferably up to about 97 weight % of the polymercontains repeating ethylene terephthalate units of the formula: ##STR1##with the remainder being minor amounts of ester-forming components. Italso includes copolymers of ethylene terephthalate wherein up to about10 mole percent of the esterifying glycol units are derived fromdiethylene glycol; propane-1,3-diol; butane-1,4-diol; polytetramethyleneglycol; polyethylene glycol; polypropylene glycol;1,4-hydroxymethylcyclohexane and the like, and up to 10 mole percent ofthe acid component is derived from acids such as isophthalic; bibenzoic;naphthalene 1,4- or 2,6-dicarboxylic; adipic; sebacic; anddecane-1,1-dicarboxylic acids and the like.

Polyethylene terephthalate should have an inherent viscosity (1%concentration of polymer in a 37.5/62.5 weight percent solution oftetrachloroethane/phenol, respectively, at 30° C.) of at least 0.55 toobtain the desired end properties in the formed articles. Preferably theinherent viscosity is at least about 0.7 to obtain an article havingexcellent toughness properties, i.e. resistance to impact loading. Theinherent viscosity of the polymer solution is measured relative to thatof the solvent alone and is defined as follows: ##EQU2## where C is theconcentration expressed in grams of polymer per 100 milliliters ofsolution.

Formation of containers with biaxial orientation according to thisinvention occurs when the outside surface temperature of thethermoplastic material of the preforms is between about 180° to about230° F. (82.2° to 110° C.) and preferably about 37° F. (93.3° C.) abovethe glass transition temperature of the material, the latter being about162° to about 165° F. (72.2° to 73.9° C.) for PET.

The following examples are given to illustrate the principles andpractice of this invention and should not be construed as limitationsthereof.

EXAMPLE I

Containers of rectangular cross section throughout the entire length,identical in form to bottles 12 in FIG. 4, are formed from reheated,cylindrical, injection molded preforms. Such containers have 24 ounces(710 cc.) nominal capacity, a weight of 48 gms., a major diameter (18 inFIG. 5) of 3.3 inches (8.4 cms.) a minor diameter (16 in FIG. 5) of 2.7inches (6.88 cms.), a total length of 7.88 inches (20.0 cms.) a circulardeviation ratio (18 divided by 16 in FIG. 5) of 1.22 and a cornerdefinition ratio (18 divided by R₁ in FIG. 5) of 13.2.

PET having an inherent viscosity of about 0.72 was injection molded inconventional equipment into preforms configured as shown at 10 in FIG. 4having the following dimensions:

total length=7.0 inches (17.7 cms.);

finish length=0.57 inches (1.45 cms.);

minimum outside diameter=1.131 inches (2.873 cms.); and

average thickness=0.102 inches (0.259 cms.)

(Average thickness is defined as minimum thickness along the length ofthe preform below the finish plus maximum thickness along such lengthdivided by two). With cavity dimensions of a blow mold set to providethe above bottle configuration, the percentages of axial stretch andradial stretch were calculated at 13.3 and 192% respectively as follows:##EQU3##

While rotating about their lengthwise axes, the body portions of suchpreforms (13 in FIG. 4) are heated from substantially room temperatureto about 200°-230° F. (93° to 110° C.) in accordance with a heatingarrangement shown in FIG. 3 of U.S. Pat. No. 4,036,927, the content ofcol. 6, lines 29-53 of which is incorporated herein by reference.

The heated preforms are introduced to a stretch-blow assembly asillustrated in FIG. 6 which included a mold cavity having a surfacecorresponding in shape and extent to that of the desired end bottleconfiguration and which is conventionally cooled via circulating waterat cooling water temperature on the order of 21° C. The preforms arethen stretched axially against the base of such cavity and expandedalong the major and minor axes into heat exchange contact with the sidewalls to form the bottle shape.

All of the bottles in the foregoing run completely conform to the moldsurfaces in the corner areas of the rectangular shape.

EXAMPLE 2

The forming procedure of Example 1 is repeated except that the totalpreform length is reduced from 7.0 to 5.5 inches (14 cms.). Averageaxial stretch is 47% while maximum radial stretch along the major axisis 189%. Each of the bottles formed conformed to the mold surfaces fullyin the corner areas of the rectangular shape.

EXAMPLE 3

The bottle mold of Example 1 is revised to provide a corner definitionratio of 17.6 and the forming procedure of Example 1 is then repeated.In each case the plastic in the corner areas of the rectangular crosssections failed to fully conform to the mold cavity surface.

Data from the foregoing Examples is used to form FIGS. 1 and 2.

The preceding Examples illustrate that when the circular deviation andcorner definition ratios lie within the crosshatched area of FIG. 1 andthe corner definition ratio to percentage axial stretch relationship iswithin the crosshatched portion of FIG. 2, good corner definition andmaterial distribution is obtained at maximum percentage radial stretchlevels no greater than about 334.

Though preforms forming the containers of this invention are preferablycircular in cross section and are not purposely provided with atemperature differential in the circumferential direction prior toexpansion in the blow mold in order to reduce the complexity of thepreform heat treating process, it is within the scope of the inventionto utilize non-cylindrical preforms heat treated to purposely develop atemperature gradient around the periphery prior to stretching in theblow mold. Preforms usable in the invention may be shaped by any wellknown plastic shaping technique such as injection or blow molding,thermoforming form sheet material with or without mechanical assist,compression molding and the like including combinations of theforegoing.

Various modifications and alterations will be readily suggested topersons skilled in the art. It is intended, therefore, that theforegoing be considered as exemplary only and the scope of the inventionbe ascertained from the following claims.

What is claimed is:
 1. In the method of forming a molecularly orientedhollow article having a substantially rectangular cross section from apreform of thermoplastic material, which includes distending the preformin a mold while at molecular orientation temperature,the improvementswherein the thermoplastic material is moldable polyalkyleneterephthalate having an inherent viscosity of at least about 0.55, saidpreform region forming said cross section is not treated before saiddistending for the purpose of establishing a circumferential temperaturedifference therein, and the distending comprises, in combination, thesteps of: expanding first portions of said region against mold wallportions at the end of a minor axis of a cavity conforming to saidsubstantially rectangular cross section to form relatively thicksections thereat while expanding other portions a greater extent thansaid first portions toward wall portions at the end of a major axis ofsaid cavity thereby establishing a strain hardened pattern in thematerial wherein such expanded other portions are strain hardenedgreater than said thick sections; and drawing material out of said thicksections as such expanded other portions of greater strain hardenedlevel continue to expand toward the mold wall portions at the end of themajor axis; limiting the corner definition ratio to between about 2 toabout 14 and the circular deviation ratio to no greater than about 2.4at the cross section during said distending; and controlling saiddistending according to the relations: ##EQU4## wherein: A is betweenabout 5 to about 100; andB is no greater than about 334; thereby formingsaid article having reduced wall thickness variability at thesubstantially rectangular cross section in comparison with an articlehaving the same cross section formed of thermoplastic material whichdoes not strain harden during distension.
 2. The method of claim 1wherein the preform comprises a major proportion of polyethyleneterephthalate.
 3. The method of claim 2 wherein the inherent viscosityof the PET is at least about 0.7.
 4. The method of claim 1 or 2 whereinthe preform is injection molded and is substantially circular in crosssection.
 5. The method of claim 4 wherein the preform is distendedagainst surfaces of a mold cavity having a heat insulative coatingthereon.
 6. The method of claim 4 wherein the article is a container. 7.The method of claim 6 wherein the container has a square cross section.8. The method of claim 7 wherein the container has a nominal capacity ofbetween about 470 to about 1890 cc.
 9. The method of claim 1 wherein thesubstantially rectangular cross section is rectangular and the articleis a container.